AVS 46th International Symposium
    Plasma Science and Technology Division Thursday Sessions
       Session PS2-ThA

Paper PS2-ThA9
Substrate and Plasma Heating within High Frequency Bi-polar Pulsed-DC Magnetron Sputtering Applications

Thursday, October 28, 1999, 4:40 pm, Room 609

Session: Pulsed Plasmas
Presenter: L.J. Mahoney, Advanced Energy Industries
Authors: L.J. Mahoney, Advanced Energy Industries
G.W. McDonough, Advanced Energy Industries
D.C. Carter, Advanced Energy Industries
G.A. Roche, Advanced Energy Industries
H.V. Walde, Advanced Energy Industries
Correspondent: Click to Email
Bipolar pulsed-DC power supplies have been developed and widely used for magnetron sputtering applications where periodic reversal of the sputter target polarity is used to suppress arc events. Pulsed-DC sputter deposition is particularly advantageous with reactive sputter deposition of oxides and select nitrides where arcs can lead to defects in deposited films and coatings. Recent technical advances now allow workers to widely adjust pulsed-DC operation by varying the pulse frequency up to 350 kHz and by varying the pulse-width or duty cycle. We have observed that at frequencies substantially greater than 100 kHz, the rate of change in substrate temperature substantially increases, a condition that can influence deposition processes. To better understand the mechanisms driving the increase in substrate heating, we examine the downstream sputter-deposition region of a closed-field magnetron with six inch diameter Al target by means of (1) fast-response thermal probes to measure the intrinsic power flux to grounded and floating substrates, (2) a time-resolved Langmuir probe to elucidate electron heating dynamics, and (3) analysis of the unique magnetron current and voltage waveforms. At pulsed-DC frequencies above 100 kHz, we observe that the intrinsic power flux density and electron density at the substrate both increase over DC and near DC sputter conditions. The measurements also indicate that the heating effect may be controlled by varying the pulsed-DC frequency and duty cycle. Moreover the heating effect correlates with transient features in the pulse-DC voltage waveform. From this work we infer that the mechanism for heating is likely to be driven by stochastic heating of the plasma electrons through a spatially-varying and time-dynamic sheath at the target, as analogous to conventional AC plasma sources. Potential process benefits of pulsed-DC operation at such high frequencies are also discussed.